NATURAL-KILLER-CELL ACTIVITY IN VERY-LOW-BIRTH-WEIGHT INFANTS

The exact role of natural killer (NK) cells in host defense is unclear , but they may be important as an early response to certain infections . We evaluated NK cell phenotype and activity in premature very low bi rth weight infants (VLBWI) (n = 52) with an average gestational age of 29.3 wk (24-35 wk) and an average birth weight of 1124 g (537-1480 g) . All patients initially were evaluated within 7 d of birth. Samples a lso were obtained at 2, 4, and 6 wk in some infants. The proportion of mononuclear cells expressing the phenotypic marker of NK cells (NKH-1 ; CD56) was significantly lower in VLBWI than in adults (2.5 +/- 1.4 V ersus, 12.5 +/- 7.8%, p < 0.0001) or term infants (2.5 +/- 1.4 versus 9.5 +/- 7.1%, p < 0.0001). VLBWI also had signifIcantly diminished NK activity expressed as the percentage of specific lysis compared with a dults (4.7 +/- 4.4 versus 32.3 +/- 14.5%, p < 0.0001 ) or term infants (4.7 +/- 4.4 versus 15.5 +/- 10.8%, p < 0.0001). Both the number of c ells expressing the NK phenotype and the NK lytic activity in VLBWI in creased in the 6 wk after birth. NK activity in VLBWI was enhanced by IL-2 and in most cases by interferon-gamma.